Re: merging two independant Java programs into one Java program running two threads?

From:

Knute Johnson <eternal@knutejohnson.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 27 Oct 2014 08:09:57 -0700

Message-ID:

<m2ln7h$oup$1@dont-email.me>

On 10/27/2014 06:33, John wrote:

Hi:

I have two independent Java programs. Program A is a GUI program.
Program B continuously take screen shots every 5 seconds and save
them into PNG picture files.

Right now, I start running Java Program B first, then start Program
A, doing GUI interaction etc.

I hope to merge the two into one Java program which runs the original
two programs by two interdependent processes or threads(not sure
which one is correct. Help please). And I would like to have this
feature: when GUI interaction by me proceeds to certain stage, e.g.
when I click Button 'XYZ' on the GUI, the process/thread taking
screen shots halts. After a while, when I click another button, the
halted process/thread proceeds again. At the end, when I quit the GUI
program, the process/thread taking the screen shots ends as well.

I think this makes me learn multi-thread programming or inter-process
communication. If you could shed some light on this project, I would
greatly appreciate it.

Thank you very much.

Eric gave you a good discussion of the issues. This is just a simple
example of starting and stopping a Thread to do a second task in your
GUI program.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class test2 extends JFrame implements ActionListener, Runnable {
     private final JMenuItem startstop;
     private final JTextArea textArea;

     private volatile Thread thread;
     private boolean runFlag;

     public test2() {
         addWindowListener(new WindowAdapter() {
             public void windowClosing(WindowEvent we) {
                 stop();
                 dispose();
             }
         });

         JMenuBar mb = new JMenuBar();
         setJMenuBar(mb);
         JMenu file = mb.add(new JMenu("file"));

         startstop = file.add("start");
         startstop.addActionListener(this);

         textArea = new JTextArea("");
         JScrollPane scrollPane = new JScrollPane(textArea);
         add(scrollPane,BorderLayout.CENTER);

         setSize(400,300);
         setLocationRelativeTo(null);
         setVisible(true);
     }

     public void actionPerformed(ActionEvent ae) {
         switch (ae.getActionCommand()) {
             case "start":
                 textArea.append("start\n");
                 startstop.setText("stop");
                 start();
                 break;
             case "stop":
                 textArea.append("stop\n");
                 startstop.setText("start");
                 stop();
                 break;
         }
     }

     public void start() {
         runFlag = true;
         thread = new Thread(this);
         thread.start();
     }

     public void run() {
         while (runFlag) {
             // do your thing
             EventQueue.invokeLater(new Runnable() {
                 public void run() {
                     textArea.append("running\n");
                 }
             });
             try {
                 Thread.sleep(1000);
             } catch (InterruptedException ie) {
                 EventQueue.invokeLater(new Runnable() {
                     public void run() {
                         textArea.append("sleep interrupted\n");
                     }
                 });
             }
         }
     }

     public void stop() {
         runFlag = false;
         thread.interrupt();
     }

     public static void main(String... args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 new test2();
             }
         });
     }
}

--

Knute Johnson